FR2768078A1 - Maintenance station for ink jet print head in franking machine - Google Patents

Abstract

The ink jet head maintenance station has a cover (226a,b) to protect the print head, cleaning pins (252a,b) to clean the print head, and a suction coupling (238a,b) to draw ink up to the level of the print head when a new cartridge has been fitted. The cover, cleaners and aspiration are activated by a single common electric motor (234). The cover is displaced by the motor and is spring-loaded (230). The cleaner is a rake that moves transversely over the face of the print head.

Description

Field of the invention
The present invention relates to the field of ink jet printing and more particularly that relating to maintenance stations for ink jet print heads of franking machines.

Prior art
With inkjet technology, especially in the field of postage where the printed postal imprint represents a monetary value, the critical problem of the print quality provided by the print head (more precisely the ejection nozzles of this head). This quality depends essentially on the care taken in the maintenance of the print head and in particular on the protection implemented for this head outside the printing phases. In fact, in the absence of special protections, the ejection nozzles are subjected to air and ambient dust, which has the consequence of causing drying and contamination of the ink contained in the head and in the supply ducts of this head. This results in a significant deterioration in the print quality.

 In French patent application FR 2 744 059, the applicant has proposed a hooding device to protect the printing module during accidental cuts in the supply which would have the consequence of leaving the heads unprotected. Another example of such a protection device is given by application FR 2 743 332 also filed in the name of the applicant.

 With French patent application FR 2 744 060, the applicant has disclosed a first type of maintenance device provided with means for periodically cleaning the heads by scraping them outside of the printing phases. The efficiency of this head and its lifespan are thus improved and the print quality is made reliable by such regular maintenance.

 In addition, it is known from international application WO 96/15908 a cleaning and capping station intended for a print head of a printing machine of the ink jet type. The cleaning device by displacement of a scraper is actuated by an electric motor while the device for protecting the heads by displacement of a hermetic cap is actuated independently by a hydraulic motor of the suction pump type.

Definition and object of the invention
The present invention provides a maintenance station which provides protection and periodic cleaning of the printheads but also which makes it possible to carry out an aspiration of the ink at the level of these heads, for example, during priming of these heads. before a first impression. An object of the invention is to carry out these three functions in a single structural unit and despite everything simple and reliable. Another object of the invention is to minimize the disadvantages for printing due to the relative movements between the print head and the maintenance station. Yet another object of the invention is to use the priming function to ensure intensive cleaning of the printheads.

 These aims are achieved by a maintenance station for an inkjet print head of a franking machine comprising first means for protecting the print head, second means for cleaning the print head, and third means to achieve ink suction at the print head, these first, second and third means being actuated from a common motor means.

 Thus the maintenance station according to the invention makes it possible to carry out the three functions of cleaning, protection and priming of the printheads in a single structure, which however is not particularly complex because these functions are carried out from '' a common engine.

 The protection means comprise a cap mounted on a support means, the displacement of this support means between a first position set back from the print head and a second position in contact with the print head being effected by monitoring a first cam profile under the action of the common motor means.

 In a preferred embodiment, the protection means are connected to the support means through an intermediate support which can move vertically over a small clearance, against intermediate spring means. Preferably, the first cam profile has an intermediate stop position corresponding to a scraping of the print heads and the cleaning means then comprise a scraper mounted on the intermediate support and whose displacement in front of the print head results from the transverse displacement of the printing module under the action of the common motor means.

 The suction means comprise a piston which can move in a cylinder, and a suction conduit disposed between this cylinder and the cap, the displacement of the piston between a first position for sucking the ink contained in the head. printing and a second position for discharging this ink towards a recovery tank also connected to this cylinder being effected by following a second cam profile under the action of the common motor means.

 In the preferred embodiment, the second cam profile is produced at the support means.

 In another embodiment, the piston is advantageously provided with a central bore for the passage of ink from the cylinder to the recovery tank. Likewise, it may include a spring-loaded valve for regulating the pressure in the cylinder. And, preferably, the ink recovery tank also functions as an ink supply tank.

 In this embodiment, the cleaning means then comprise a lever articulated to the support and provided at its end with a scraping element, the displacement of this lever being effected as a function of the joint rotation of the first and second cams controlled by the common motor means.

Brief description of the drawings
Other characteristics and advantages of the present invention will emerge more clearly from the following description, given by way of non-limiting illustration, with reference to the appended drawings, in which: - Figure 1 is a block diagram of a first embodiment of a maintenance station according to the invention, - Figures 2 and 3 show the maintenance station of Figure I in two successive positions corresponding to a protective position and a priming position of the print heads, and - Figures 4 and 5 show this maintenance station in two other positions corresponding to cleaning of the print heads, - Figure 6 is a block diagram of a second embodiment of a maintenance station according to the invention , FIGS. 7 and 8 show the maintenance station of FIG. 6 in two successive positions corresponding to a position before maintenance and a position for protecting the print heads, and - Figures 9 and 10 show this maintenance station in two other positions corresponding to a priming position and a cleaning position of the print heads.

Detailed description of preferred embodiments
Let us examine Figure 1 which shows a maintenance station according to the invention in a first embodiment. This station is arranged under the movable table 10 (which can for example be moved by means of the oscillating supports not shown) of a franking machine, at the level of its printing module 12. The printing module can comprise one or more printheads, for example two heads 120a, 120b. Each head is conventionally formed of a linear network of ejection nozzles distributed according to a variable resolution, typically from 100 to 300 nozzles per cm, and each of which selectively ejects ink to achieve the printing of a postal imprint on an envelope or a label 14 running under the print heads 120a, 120b, in a direction D, between the movable table 10 and a fixed guide plate 16.

The print heads are supplied with ink from one or more ink supply reservoirs, for example a cartridge 18, through supply conduits 19a, 19b. The table 10 and the guide plate 16 are provided to the right of the print heads with openings 20a, 20b to allow the station to move.

 The maintenance station comprises mounted on a frame 22 at least one support means 24a, 24b on which is mounted a means for protecting the print head advantageously formed by a cap 26a, 26b made dustproof by means of a elastomeric seal. The support means can move vertically relative to the frame by following a first carne profile 28 which acts on a first shaft 32 integral with this support means. The cam is rotated about a first axis of rotation 30 by a motor means 34, advantageously a stepping drive motor or any similar electric motor. First spring means 36 disposed between this first shaft 32 and the frame 22 act against the action of the cam 28 for, in a rest position (and preferably also in the event of a cut in the supply of the motor drive), press the protective means 26a, 26b against the print head 120a, 120b.

 The support means 24a, 24b is advantageously in the form of a cylinder closed at one end and in which can slide a piston 38a, 38b provided with a central bore 40a, 40b in communication with an ink recovery tank provided a non-return valve 41a, 41b. Preferably, this reservoir which can be in the form of a recovery foam (the non-return valve is then disposed at the outlet of the bore 40) or even of a cartridge, can be constituted by a part of the reservoir ensuring the ink supply to the print heads (for example the cartridge 18 then provided with a partition wall 180). The head of the piston has a spring valve 42a, 42b for conventionally regulating the pressure in the chamber in front of the piston to a predetermined value. The piston cylinder has at its periphery an orifice 44a, 44b to which is connected a first end of a flexible suction duct 46a, 46b, the second end of which is fixed to the protective means 26a, 26b and through which goes drain the ink during the suction or priming phase. The piston can move vertically in the cylinder following a second cam profile 50 which acts on a second shaft 52 integral with the piston. The cam 50 is rotated around a second axis of rotation 48 and as the cam 28 is driven by the drive motor 34. Second spring means 54 disposed between this second shaft 52 and the frame 22 act at the counteracting the action of the cam 50 in order to, in a rest position (but also in the event of a cut in the supply to the drive motor), allow the piston to return to its initial rest position.

 Position detectors 56, 58, mechanical or optronic, are provided at each cam 28, 50 to allow precise determination of an origin or rest position from which the supports 24a, 24b and the pistons will be moved. 38a, 38b. Similarly, the station includes a cartridge presence detector 60 to prevent the priming phase from being carried out while the reservoir for recovering excess ink is not in place. These detectors each deliver an information signal for a control means (not shown; it may be the microprocessor of the franking machine or a processor specially dedicated to the maintenance station) which will develop the control of the motor means. 34, in particular on the basis of this information.

 A cam track 64a, 64b produced in the frame 22 (or in any other part integral with this frame) is also provided to cooperate with a lever 66a, 66b provided at one end with a cleaning means 68a, 68b of the print head (preferably a scraper brush). This lever can move in the cam path against third spring means 74a, 74b mounted between the lever 66 and the support means. The lever pivots about a hinge pin 70a, 70b fixed to the support means 24a, 24b. A stop arm 72a, 72b secured to the second shaft 52 is closed off the cam path when the cam 50 is in a high position, preventing action of the cleaning means.

 The operation of the maintenance station is as follows. It will be assumed that when the franking machine is started, the maintenance station is in any position.

 The first operating phase of the station therefore consists in bringing this station into a high position corresponding to a protection of the printing heads and illustrated in FIG. 1. For this, the drive motor 34 is controlled by the control means to rotate in a first direction of rotation in order to bring (following the first cam profile 28 which rotates in synchronism) the support means 24a, 24b to an initial initial position (zero position of the detector 58) corresponding to the setting in contact with the protection means 26a, 26b with the print heads 120a, 120b. Contact is facilitated by the action of the first spring means 36 acting in the same direction. The pistons of the support means are then in a position such that the chambers in front of the pistons are at atmospheric pressure and are not in connection with the suction conduits 46a, 46b which are in fact closed by the heads of the pistons.

 The second operating phase can then begin (Figure 2). This is the suction phase of the ink contained in the print heads and in the supply conduits (these are conduits 19a, 19b placed between the ink tank and the ink heads. impression). This phase, also known as the priming phase, must be carried out each time the ink supply tank is changed. For this, the motor 34 is now actuated by the control means in a second direction of rotation, opposite to the previous one, in order to cause a displacement of the pistons 38a, 38b (via the second shaft 52 and the second cam profile 50 which rotates in synchronism) in a first direction (preferably a descending direction). During this descent, the suction conduits 46a, 46b initially closed, as mentioned above, are placed in communication with the chambers of the pistons and, under the effect of the pressure difference existing between the chamber and the corresponding conduit, l ink is sucked into the chamber (withdrawal of the piston leads to a vacuum in the chamber which is regulated by the valve 42a, 42b). A new action on the drive motor 34 allows displacement of the piston 38a, 38b in an opposite direction (FIG. 3) and concurrently the discharge of the ink towards the recovery cartridge 18 (through the central bore 40a , 40b of the piston). This double suction / evacuation operation can be repeated several times to ensure complete emptying of the ink. During this entire phase, the non-return valve 41a, 41b prevents air from entering the chamber by preventing the pressure inside it from exceeding atmospheric pressure.

 The third operating phase corresponds to a cleaning phase of the printheads which it is preferable to carry out after each priming phase. However, this phase can also be controlled according to the wishes of the user. It begins with a descent of the support means 24a, 24b (FIG. 4) following a first rotation of the cam 28, the first profile of which acts on the first shaft 32. The stop arm 72 always closes the cam path 64 but the cleaning lever 66 is now in the position of being released. This release is effected by the combined action of the third spring means 74 and the second cam 50 which, by acting on the second shaft 52 by its second profile, lowers the stop arm 72 secured to this shaft. The lever 66 will then move from its original position to a second position and scrape the print head (Figure 5). A joint rotation of the first and second cams 28, 50 then has the effect of forcing the lever 66 to follow the cam path 64 along the arrow F to its original position and to replace the stop arm 72 in its closed position of the cam path (Figure 4).

 Reference is now made to FIG. 6 which schematically illustrates a second preferred embodiment of the maintenance station according to the invention.

 The station which is shown in this figure in a printing position is arranged under a movable table 210 of a franking machine, set back from its printing module 212, transversely to the direction D of movement of the mail items to postage (envelopes or labels 214).

The printing module may include one or more printheads, for example two heads 2120a, 2120b. As in the previous example, each head is conventionally formed of a linear network of ejection nozzles distributed according to a variable resolution, typically from 100 to 300 nozzles per cm, and each of which selectively ejects ink to achieve the printing of a postal imprint on the mail item passing under the print heads between this movable table and a fixed guide plate 216. The print heads each have in this embodiment an ink supply tank integrated 218a, 218b.

 The maintenance station comprises mounted on a fixed frame 222 a support means 224 on which are mounted means for protecting the print heads advantageously formed by caps 226a, 226b made dust-tight by means of elastomeric seals. The protection means are connected to the support means through an intermediate support 228 which can move vertically over a small clearance, against intermediate spring means 230. The support means which advantageously takes the form of a carriage movable transversely to direction D can move vertically between a first position in which the protective means are set back from the print heads and a second position in which they are in contact with these print heads , the movement between these two positions being effected by following a first cam profile 232 (profile sloping advantageously from 25 to 45 "with an intermediate stop position at 00) under the action of a common motor means 234, advantageously a stepping drive motor or any other similar electric motor. First spring means 236 (of traction type) disposed between the hub in support 224 and the frame 222 allow the return tracking of the first cam profile 232.

 A cylinder 240a, 240b integral with the frame 222 and in which a piston 238 can move is connected on the one hand to the cap 226a, 226b by a flexible suction duct for example in the form of Y 246 and on the other hand to a ink recovery tank (through a non-return valve 242). Preferably, this reservoir may be in the form of a recovery foam 244 or else of an independent cartridge to which the non-return valve is then integrated directly. The piston can move in the cylinder, between a first position of suction of the ink contained in the print head and a second position of evacuation of this ink towards the recovery tank, this displacement being carried out under the action of the common motor means 234 by following a second cam profile 250 produced in the support means 224 and against second spring means 254 (of compression type).

 It will also be noted that the printing module is provided with at least one stop 248a, 248b intended to cooperate with the support means 224 to define a scraping stroke for cleaning the printing module by scrapers 252a, 252b (a by print head) mounted on the intermediate support 228.

 Of course, mechanical or optronic position detectors (not shown) are provided at the level of the maintenance station in order to determine with precision an original position, or rest position, from which the support means will be moved. 224 and the piston 238. Similarly, when it includes a recovery tank, the station is advantageously provided with a detector for the presence of this tank (not shown) to prevent the suction phase from being carried out while the ink recovery tank is not in place. These detectors each deliver an information signal for a control means (not shown; but it can be the microprocessor of the franking machine or a processor specially dedicated to the maintenance station) which develops the control of the means engine 234, in particular on the basis of this information.

 The operation of the maintenance station in the second embodiment can be described as follows. First of all, it is advisable to bring the printheads to this station, that is to say to move the printing module from its initial printing position (FIG. 6) to a maintenance position ( figure 7). For this, the drive motor 234 is controlled by the control means to rotate in a first direction of rotation in order to bring the printing module 212 (for example via a screw-nut system integral with the printing module) in abutment 248b against the support means 224.

The protection means are not in contact with the print heads and the piston 238 is in a position such that the chamber of the piston behind the piston is not in connection with the suction duct 246.

 Protection of the printheads is then obtained by continuing to rotate the motor 234 which, by causing the print module 212 to move again, causes the support means 224 to rise according to the first cam profile 232. This movement of the support allows a simultaneous movement of the piston 238 (under the pressure of the second spring means 254), which has the effect of generating a vacuum in the chamber of this piston. During this entire phase, the non-return valve 242 prevents air from entering the chamber. At the end of the cam profile, the protection means are pressed against the print heads (Figure 8). The intermediate support 228 and the associated intermediate spring means 230 make it possible to adjust the pressure force of the protection means 226a, 226b to a determined value sufficient to ensure good sealing of the protection.

 A new operating phase can then begin (Figure 9). This is the suction phase of the ink supplying the print heads which can be carried out in case of real need, for example following an untimely cut in the voltage supply to these heads. For this, the motor 234 is again actuated by the control means in order to cause a new displacement of the printing module 212 which causes by its action on the support means 224 a rise of the piston 238 according to the second cam profile 250. During this rise, the suction conduit 246 is placed in communication with the chamber of the piston and, under the effect of the vacuum existing in the chamber, the ink is sucked through this conduit.

 The last operating phase corresponds to a phase of evacuation of the ink stored in the chamber and cleaning of the print heads by wiping the ejection nozzles of these heads. It occurs during a displacement in the opposite direction of the support means 224 (which is then driven by a stop 248a secured to the printing module) following a rotation also in the opposite direction of the motor 234 (FIG. 10) and under the effect of the first spring means 236. This displacement which causes the descent of the support means according to the first cam profile 232 has the effect of compressing the second spring means 254 associated with the piston 238 and, by opening the non-return valve 242, eject the ink previously sucked into the chamber towards the recovery foam 244 advantageously placed under the maintenance station. This descent stops for the first time at a scraping position in which the support means is engaged on the intermediate position of the cam profile. In this position, the motor 234 is actuated so as to again drive the printing module, the heads of which will be cleaned during their respective passage in front of the scrapers 252a, 252b. the stop 248a of the printing module will then again drive the support means 224 which will return to its original position at the first end of the cam profile 232 under the effect of the first means spring 236. The piston which continues to compressing the second spring means 254 will, during this last part of the descent, finish removing the ink accumulated in the chamber of the piston 238.

Claims (11)

 1. Maintenance station for an inkjet print head of a franking machine comprising: - first means (26a, 26b; 226a, 226b) for protecting the print head, - second means (66a, 66b ; 252a, 252b) for cleaning the print head, characterized in that it further comprises third means (38a, 38b; 238a, 238b) for carrying out an aspiration of the ink at the level of the print head (120a, 120b; 2120a, 2120b), and in that said first, second and third means are actuated from a common motor means (34,234).  2. Maintenance station according to claim 1, characterized in that said protection means comprise a cap (26a, 26b; 226a, 226b) mounted on a support means (24a, 24b; 2 24a, 224b), the movement of this support means between a first position set back from the print head and a second position in contact with the print head being effected by following a first cam profile (28; 232) under the action of the motor means common.  3. Maintenance station according to claim 2, characterized in that said protection means are connected to the support means (224) through an intermediate support (228) which can move vertically over a small clearance, against intermediate spring means (230).  4. Maintenance station according to claim 2, characterized in that said first cam profile comprises an intermediate stop position corresponding to a scraping of the print heads.  5. Maintenance station according to claim 3 or claim 4, characterized in that said cleaning means comprise a scraper ('5tua, 252b) mounted on the intermediate support (228) and whose displacement in front of the print head results transverse displacement of the printing module (212) under the action of the common motor means (234).  6. Maintenance station according to claim 1, characterized in that said suction means comprise a piston (38a, 38b; 238) which can move in a cylinder (24a, 24b; 240), and a suction duct ( 46a, 46b; 246) disposed between this cylinder and the cap, the displacement of the piston between a first position for sucking the ink contained in the print head and a second position for discharging this ink towards a reservoir of recovery (18, 244) also connected to this cylinder being effected by monitoring a second cam profile (50; 250) under the action of the common motor means.  7. Maintenance station according to claim 6, characterized in that said second cam profile is produced at the support means (224).  8. Maintenance station according to claim 6, characterized in that said piston is provided with a central bore (40) for the passage of ink from the cylinder to the recovery tank.  9. Maintenance station according to claim 6, characterized in that said piston (38a, 38b) comprises a spring valve (42) for regulating the pressure in the cylinder.  10. Maintenance station according to claim 6, characterized in that said ink recovery reservoir also acts as an ink supply reservoir (18).  11. Maintenance station according to claim 2 or claim 6, characterized in that said cleaning means comprise a lever (66a, 66b) articulated to the support (24a, 24b) and provided at its end with a scraping element ( 68a, 68b), the movement of this lever being effected by joint monitoring of the first and second cam profiles (28, 50) under the action of the common motor means (34).